1. Field of the Invention
The present invention relate to image processing techniques.
2. Description of the Background Art
Conventionally, techniques (matching point search techniques) are known in which two images are obtained by imaging the same object from different viewpoints with a so-called stereo camera and individual pixels in the two images are mutually correlated by comparison of two-dimensional image regions, e.g. by template matching.
In such matching point search techniques using two-dimensional image regions, one image is processed as a reference (reference image) and the other image is processed as a target (target image), for example. In such a matching point search technique, first, a window region is set in the reference image such that a point of interest in the reference image is approximately the gravity center position, and a window region of the same size is set in the target image such that a point to be processed in the target image is approximately the gravity center position. Then, the correlation between the two window regions is evaluated to match pixels between the reference and target images (for example, “A Sub-Pixel Correspondence Search Technique for Computer Vision Applications”, Kenji TAKITA, Mohammad abdul MUQUIT, Takafumi AOKI, and Tatsuo HIGUCHI, IEICE TRANS. FUNDAMENTALS, VOL E87-A, NO. 8 Aug. 2004, which is hereinafter referred to as Non-Patent Document 1).
Also, for such matching point search techniques, a technique is proposed in which the amount of computations required for the search of a matching point is considerably reduced and the results of matching are obtained very precisely and in short time (for example, Japanese Patent Application Laid-Open No. 2008-123141, which is hereinafter referred to as Patent Document 1). In this technique, the shape of window regions is one-dimensional. Also, a technique is proposed in which influences of noise are reduced and the three-dimensional position of an object can be very precisely measured (for example, Japanese Patent Application Laid-Open No. 208-157780, which is hereinafter referred to as Patent Document 2). In this technique, a matching point search is performed with integral images obtained by integrating individual pixels in time-sequentially taken multiple images.
In such matching point search techniques, the parallax about individual pixels between the reference image and target image is approximately uniform when the distance to the object taken in the two window regions set in the reference and target images is approximately uniform on the basis of the stereo camera, and then the matching point search offers precise results. Also, the amount of information used for the matching point search can be increased by increasing the size of window regions, and then the precision of the matching point search is ensured.
However, in the technique of Non-Patent Document 1, when the reference image and target image include a mixture of distant and near objects (distant-near competing condition), increasing the size of the window regions to ensure precise matching point search will deteriorate the precision of the matching point search.
Also, in the technique of Patent Document 1, while the size of window regions is reduced by adopting one-dimensional window regions, matching points are searched for by statistical processing using the results of evaluation over adjacent multiple lines, in order to ensure the amount of information. Accordingly, the precision of the matching point search might be deteriorated due to the distant-near competing condition.
The technique of Patent Document 2 gives no consideration at all to measures against the distant-near competing condition in matching point search.